ci: switched to source-based coverage

[ErikBjare]

Largely based on how grcov themselves do it: https://github.com/mozilla/grcov/blob/master/.travis.yml

From mozilla/grcov@e98d5dd, it seems we can go even further and remove CARGO_INCREMENTAL and RUSTDOCFLAGS.

Hopefully helps with #189

Screenshot of HTML report when I run locally. Note that source-based coverage grcov doesn't support branch coverage (I asked them about it in mozilla/grcov#520):

[ErikBjare]

Getting a better error message for the blinking macOS builds (#180):

 error[E0514]: found crate `serde_derive` compiled by an incompatible version of rustc which `serde` depends on
 --> aw-models/src/timeinterval.rs:3:5
  |
3 | use serde::de::{self, Deserialize, Deserializer, Visitor};
  |     ^^^^^
  |
  = help: please recompile that crate using this compiler (rustc 1.50.0-nightly (b48cafd9e 2020-11-25))
  = note: the following crate versions were found:
          crate `serde_derive` compiled by rustc 1.50.0-nightly (a0d664bae 2020-11-22): /Users/runner/work/aw-server-rust/aw-server-rust/target/debug/deps/libserde_derive_internals-67951bb09d951f1c.rmeta
          crate `serde_derive` compiled by rustc 1.50.0-nightly (a0d664bae 2020-11-22): /Users/runner/work/aw-server-rust/aw-server-rust/target/debug/deps/libserde_derive_internals-67951bb09d951f1c.rlib

I assume we'll have to somehow discard the cache if we're using a new compiler. Weird that cargo/rustc doesn't do this itself.

[codecov]

Codecov Report

Merging #192 (5a2690b) into master (d44b082) will increase coverage by 6.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #192      +/-   ##
==========================================
+ Coverage   53.60%   59.74%   +6.13%     
==========================================
  Files          58       42      -16     
  Lines        7687     4308    -3379     
  Branches     1821        0    -1821     
==========================================
- Hits         4121     2574    -1547     
+ Misses       3559     1734    -1825     
+ Partials        7        0       -7     

Impacted Files	Coverage Δ
aw-server/src/dirs.rs	0.00% <0.00%> (-86.05%)	⬇️
aw-transform/src/split_url.rs	10.34% <0.00%> (-80.57%)	⬇️
aw-server/src/logging.rs	0.00% <0.00%> (-71.80%)	⬇️
aw-transform/src/flood.rs	62.96% <0.00%> (-35.03%)	⬇️
aw-transform/src/heartbeat.rs	73.91% <0.00%> (-21.44%)	⬇️
aw-transform/src/find_bucket.rs	83.33% <0.00%> (-16.67%)	⬇️
aw-transform/src/filter_keyvals.rs	86.36% <0.00%> (-13.64%)	⬇️
aw-query/src/datatype.rs	72.50% <0.00%> (-9.17%)	⬇️
aw-transform/src/chunk.rs	92.00% <0.00%> (-8.00%)	⬇️
aw-query/src/functions.rs	84.39% <0.00%> (-7.59%)	⬇️
... and 48 more

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[ErikBjare]

@johan-bjareholt Why is COVERAGE_CACHE set?

Edit: Nvm, I think I get it.

[ErikBjare]

@johan-bjareholt It seems like coverage reporting is consistent now (at least from the two commits in this PR 🤞)... I will go ahead and merge this so I rebase another PR and hopefully get reasonable results.

[ErikBjare]

From looking at the rebased #185 it looks like coverage works properly now 🎉

Hoping it stays that way 🤞